Hadrosaurid phylogenetic matrix.txt from Dinosaurs from the Santonian–Campanian Atlantic coastline substantiate phylogenetic signatures of vicariance in Cretaceous North America

During the Cretaceous, diversifications and turnovers affected terrestrial vertebrates experiencing the effects of global geographical change. However, the poor fossil record from the Middle Cretaceous has concealed how dinosaurs and other terrestrial vertebrates responded to these events. I describe two dinosaurs from the Santonian to Early Campanian of the obscure North American paleolandmass Appalachia. A revised look at a large, potentially novel theropod shows that it likely belongs to a new clade of tyrannosauroids solely from Appalachia. Another partial skeleton belongs to an early member of the Hadrosauridae, a highly successful clade of herbivorous dinosaurs. This skeleton is associated with the first perinate dinosaur specimens from the Atlantic Coastal Plain. The tyrannosauroid and hadrosaurid substantiate one of the only Late Santonian dinosaur faunas and help pinpoint the timing of important anatomical innovations in two widespread dinosaur lineages. The phylogenetic positions of the tyrannosauroid and hadrosaurid show Santonian Appalachian dinosaur faunas are surprisingly comparable to coeval Eurasian ones, and the presence of clades formed only by Appalachian dinosaur taxa establishes a degree of endemism in Appalachian dinosaur assemblages attributable to episodes of vicariance.

白垩纪期间，全球地理格局变迁引发的连锁效应波及陆生脊椎动物，引发了类群的辐射分化与生态更替。然而，中白垩世的化石记录极为匮乏，掩盖了恐龙与其他陆生脊椎动物对这些地质事件的响应历程。本文记述了产自北美鲜为人知的古陆块阿巴拉契亚（Appalachia）圣通阶（Santonian）至早坎潘阶（Early Campanian）地层中的两类恐龙。对一具体型庞大、疑似为新物种的兽脚类化石进行重新研究后表明，该标本很可能隶属于一类仅分布于阿巴拉契亚的暴龙超科（tyrannosauroids）新演化支。另一具部分保存的骨骼则属于鸭嘴龙科（Hadrosauridae）的早期类群——该类群是一类演化极为成功的植食性恐龙类群。该骨骼标本与大西洋沿岸平原迄今发现的首批恐龙围产期标本共存出土。这两类暴龙超科与鸭嘴龙科标本，是目前已知的为数不多的晚圣通阶（Late Santonian）恐龙动物群之一，它们有助于精准确定两个广泛分布的恐龙支系重要解剖学特征演化出现的时间节点。系统发育分析结果显示，圣通阶阿巴拉契亚恐龙动物群与同时期的欧亚大陆恐龙动物群具有出人意料的相似性；而仅由阿巴拉契亚恐龙类群构成的演化支的存在，则证明阿巴拉契亚恐龙组合存在一定程度的特有性，这一现象可归因于地理隔离事件引发的分化。